Muffler for engine

ABSTRACT

A muffler for an engine is provided. A muffler ( 50 ) according to an embodiment of the present invention includes a box-shaped housing ( 51 ), and a partition ( 56 ) that divides the inside of the housing ( 51 ) into a first chamber ( 61 ) and a second chamber ( 62 ). The partition ( 56 ) includes a main body portion ( 56   a ) in the form of a flat plate, and a concave portion ( 56   b ) that protrudes toward the second chamber ( 62 ). Exhaust gas, having flowed from an inlet ( 52   a ) of the housing ( 51 ) into the first chamber ( 61 ), passed a through hole ( 57 ) of the main body portion ( 56   a ), and reached one side in the second chamber ( 62 ), flows inside the second chamber ( 62 ) so as to bypass a second concave portion ( 56   b   2 ) of the concave portion ( 56   b ) and then passes the other side in the second chamber ( 62 ) to reach an outlet ( 53   a ) of the housing ( 51 ).

CROSS-REFERENCE TO RELATED APPLICATION

The application claims priority to Japanese Patent Application No. 2016-087945 filed on Apr. 26, 2016, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a muffler for an engine (internal combustion engine).

2. Description of Related Art

A muffler for an engine installed in a portable work machine such as a brush/weed cutter includes a box-shaped housing having, for example, an inlet that is connected to an exhaust port of the engine to allow exhaust gas to flow in, and an outlet for discharging the exhaust gas having flowed in. The inside of the housing is divided by a partition into a first chamber with the inlet and a second chamber with the outlet. The partition has plural through holes that communicate between the first and second chambers. Such engine muffler is disclosed in JP 2014-181580 A.

In the muffler disclosed in JP 2014-181580 A, however, the substantial distance the exhaust gas has to flow (move) from the through hole of the partition to the outlet of the housing is relatively short. This makes it difficult to efficiently reduce the pressure of the exhaust gas within the second chamber, and resultantly achieve a satisfactory noise-reduction effect of the muffler.

SUMMARY OF THE INVENTION

In view of the above circumstances, the present invention has been accomplished and an object of the present invention is to enhance the noise-reduction effect of the muffler.

According to a first aspect of the present invention, there is provided a muffler for an engine, which includes: a box-shaped housing having an inlet that is connected with an exhaust port of the engine to allow exhaust gas to flow in, and an outlet for discharging the exhaust gas having flowed in; and a partition for dividing the inside of the housing into a first chamber with the inlet and a second chamber with the outlet. The partition includes a main body portion in the form of a flat plate, and a concave portion that protrudes toward the second chamber from the main body portion. The main body portion has, on one side thereof, at least one through hole that communicates between the first and second chambers. At least a portion of the bottom of the concave portion contacts an inner surface of the second chamber in the housing. Exhaust gas, having flowed from the inlet into the first chamber, passed the through hole, and reached one side in the second chamber, flows inside the second chamber so as to bypass the concave portion and then passes the other side in the second chamber to reach the outlet.

According to a second aspect of the present invention, there is provided a muffler for an engine, which includes: a box-shaped housing having an inlet that is connected with an exhaust port of the engine to allow exhaust gas to flow in, and an outlet for discharging the exhaust gas having flowed in; a partition for dividing the inside of the housing into a first chamber with the inlet and a second chamber with the outlet; and a flow regulating part for partially regulating the flow of exhaust gas inside the second chamber. The partition has, on one side thereof, at least one through hole that communicates between the first and second chambers. Exhaust gas, having flowed from the inlet into the first chamber, passed the through hole, and reached one side in the second chamber, flows inside the second chamber so as to bypass the flow regulating part and then passes the other side in the second chamber to reach the outlet.

Other objects and features of aspects of the present invention will be understood from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a brush/weed cutter according to an embodiment of the present invention.

FIG. 2 is an explanatory view of the brush/weed cutter in use according to the embodiment.

FIG. 3 is a schematic cross-sectional view of an engine and a muffler according to the embodiment.

FIG. 4 is a front view of the muffler according to the embodiment.

FIG. 5 is a cross-sectional view of the muffler taken at line I-I in FIG. 4.

FIG. 6 is a cross-sectional view of the muffler taken at line II-II in FIG. 4.

FIG. 7 is a front view of a partition according to the embodiment.

FIGS. 8A and 8B illustrate the flow of exhaust gas in the muffler according to the embodiment.

FIGS. 9A and 9B illustrate the flow of exhaust gas in the muffler according to the embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view of a brush/weed cutter according to an embodiment of the present invention. FIG. 2 is an explanatory view of the brush/weed cutter in use. Note that in the present embodiment, the brush/weed cutter is illustrated as an example of a portable work machine in which a muffler for an engine of the present invention is installed, but the muffler for an engine of the present invention can be installed in any other portable work machines.

A brush/weed cutter 1 includes an operation shaft 2 in the form of a long pipe. An engine module 3 is provided as a power source at the rear end of the operation shaft 2. A tool attachment base 4 is disposed, as a working portion, at the tip of the operation shaft 2.

The tool is replaceably attached to the tool attachment base 4. The tool attachment base 4 is connected to the engine module 3 by means of a drive shaft incorporated in the operation shaft 2. The tool attachment base 4 is rotated by the engine module 3 (more specifically, an engine 21).

A handle 5 is attached at the center of the operation shaft 2 in its longitudinal direction. A vibration-proofing housing 6 is disposed between the handle 5 and the engine module 3. A hanger 7 is provided around the outer periphery of the vibration-proofing housing 6.

The brush/weed cutter 1 is slung by a holder 8 over the shoulder of an operator M. The holder 8 includes a harness 9 and a loop 10. The operator M wears the harness 9 on his upper body. In FIG. 2, the loop 10 is hung on the right side of the operator M. The operator M hooks the hanger 7 over the loop 10 and operates the thus-suspended brush/weed cutter 1. The operator M grips the handle 5 of the brush/weed cutter 1 with his hands and moves the brush/weed cutter 1 to cut weeds.

The engine module 3 is mainly composed of a cover 11 as its armor, the engine 21 covered with the cover 11 (see FIG. 3 as below), and a muffler 50. Here, the muffler 50 corresponds to a “muffler for an engine” of the present invention. The cover 11 is made of, for example, resin.

FIG. 3 is a schematic cross-sectional view of the engine 21 and the muffler 50. FIG. 3 illustrates the engine 21 in case a piston 25 is positioned near a top dead center. Furthermore, in the present embodiment, the term “upper side” substantially corresponds to a vertically upper side of the engine 21 in such a posture that the engine 21 stands (upright posture), when in use, for the longest period of time.

The engine 21 is an overhead valve (OHV) 4-stroke, air-cooled engine. The engine 21 has a cylinder part 22, a crank case 23 disposed below the cylinder part 22, and an oil tank 24 disposed below the crank case 23.

The cylinder part 22 has cylindrical space through which the piston 25 slidably moves in the vertical direction in FIG. 3. The piston 25 is inserted into the space with a clearance that allows vertical sliding in FIG. 3.

The cylinder part 22, the crankcase 23, and the piston 25 constitute a crank chamber 27. More specifically, the cylindrical space on the crankcase 23 side as defined by the side surface of the cylinder part 22 and the piston 25 and the internal space of the crankcase 23 form the crank chamber 27. In the crank chamber 27, its internal volume changes along with the sliding movement of the piston 25.

The cylinder head 28, the cylinder part 22, and the piston 25 constitute a combustion chamber 29. The oil tank 24 is defined by an oil tank case and provided separately of the crankcase 23. The oil tank 24 retains lubricating oil.

A check valve 30 is disposed between the oil tank 24 and the crankcase 23, which only allows oil to flow into the oil tank 24 from the crankcase 23 (crank chamber 27).

In this example, as the piston 25 moves from a bottom dead center to the top dead center, the pressure in the crank chamber 27 becomes a negative pressure. In contrast, along with the movement of the piston 25 from the top dead center to the bottom dead center, the pressure in the crank chamber 27 becomes a positive pressure. Thus, when the pressure of the crank chamber 27 is positive, the check valve 30 opens to let oil flow from the crank chamber 27 to the oil tank 24. If the pressure of the crank chamber 27 is negative, the check valve 30 closes.

A crank 33 is rotatably supported inside the crankcase 23. The crank 33 is composed of a crank shaft 33 a as the rotational center, a counter weight, etc. The piston 25 and the crank 33 are connected together by means of a connecting rod 34. The connecting rod 34 and the piston 25 are oscillatably connected. The connecting rod 34 and the crank 33 are rotatably connected. Such configuration ensures that the piston 25 reciprocates inside the cylinder part 22.

A cylinder head 28 is provided on an upper wall of the cylinder part 22. The cylinder head 28 is equipped with an intake port 35 and an exhaust port 36. The intake port 35 is in communication with a carburetor (not shown) by means of an insulator (not shown). An air cleaner (not shown) is provided upstream of the carburetor. Note that the engine module 3 further includes the aforementioned insulator, carburetor, and air cleaner, and a fuel storage tank (not shown). The above insulator, carburetor, and air cleaner are covered with the cover 11. The carburetor is a device for mixing a fuel with the air past the air cleaner to generate an air-fuel mixture.

The muffler 50 has a vertically-elongated thin form. In the present embodiment, the muffler 50 is directly connected to the exhaust port 36 of the engine 21, communicating with the exhaust port 36. The muffler 50 is detailed below with reference to FIGS. 4 to 7.

The cylinder head 28 is equipped with an intake valve 37 for opening/closing the intake port 35. Moreover, the cylinder head 28 is equipped with an exhaust valve 38 for opening/closing the exhaust port 36. The intake valve 37 and the exhaust valve 38 open/close the combustion chamber 29.

Next, the muffler 50 is described in more detail with reference to FIGS. 4 to 7 together with FIG. 3 as referenced above. FIG. 4 is a front view of the muffler 50. FIG. 5 is a cross-sectional view taken at line I-I of FIG. 4. FIG. 6 is a cross-sectional view taken at line II-II of FIG. 4. FIG. 7 is a front view of a partition (partition plate) 56. In the following, the upper and lower sides and the right and left sides are defined as illustrated in FIGS. 4 to 7 for ease of explanation. Furthermore, the intake side is defined as being on the engine 21 side, and the discharge side is defined as being opposite to the engine 21 side (i.e., on the side far from the engine 21). The “upper side” in FIGS. 4 to 7 substantially corresponds to a vertically upper side of the engine 21 in such a posture that the engine 21 stands (upright posture), when in use, for the longest period of time. Moreover, the “left side” in FIG. 4 to 7 corresponds to “one side” or “one horizontal side” of the present invention, whereas the “right side” corresponds to “the other side” or “the other horizontal side”.

The muffler 50 includes a housing 51, the partition 56, and a guide member 58. The housing 51 is provided in the form of substantially a rectangular box and composed of a first container 52 and a second container 53. In the present embodiment, the first container 52 and the second container 53 are made of metal but may be alternatively made of resin resistant to high temperature like fiber reinforced plastics (FRP), etc.

The first container 52 defines the intake side of the housing 51. The first container 52 has substantially a rectangular box shape that opens at its discharge side. The first container 52 has an external flange portion 54 that extends outward at its peripheral edge on the discharge side. An inlet 52 a is formed at an upper portion of the first container 52. The inlet 52 a is connected to the exhaust port 36. Owing to the inlet 52 a provided at the upper portion of the first container 52, the muffler 50 does not so much extend upward beyond the engine 21.

The second container 53 defines the discharge side of the housing 51. The second container 53 has substantially a rectangular box shape that opens at its intake side. The second container 53 has an external flange portion 55 extending outward at its peripheral edge on the intake side. A convex portion 53 p protrudes outward (opposite to a second chamber 62) at a somewhat lower position than the center of the second container 53 in the vertical direction. As illustrated in FIG. 4, the convex portion 53 p has a horizontally elongated rectangular form as viewed from the front. The convex portion 53 p has substantially a U shape in cross section and extends in the horizontal direction (right-left direction). The convex portion 53 p has an opening 53 q at the left end. Here, the substantially rectangular opening at the intake side end of the convex portion 53 p (i.e., the substantially rectangular opening at the proximal-end-side end of the convex portion 53 p) corresponds to the outlet 53 a. Thus, the convex portion 53 p protrudes outward to cover the outlet 53 a and also includes the opening 53 q.

The metal or resin partition 56 is composed of a main body portion 56 a in the form of substantially a rectangular flat plate and a concave portion 56 b formed at the center in the horizontal direction (right-left direction). The peripheral edge of the main body portion 56 a of the partition 56 is fixed to the first container 52 and the second container 53 by means of a swage while being clamped between the external flange portion 54 of the first container 52 and the external flange portion 55 of the second container 53. Accordingly, in the housing 51, a first chamber 61 is defined by the first container 52 and the partition 56, and the second chamber 62 is defined by the second container 53 and the partition 56. In this example, the first chamber 61 includes the inlet 52 a. On the other hand, the second chamber 62 includes the outlet 53 a. In addition, the first chamber 61 communicates with the exhaust port 36 through the inlet 52 a.

The concave portion 56 b of the partition 56 is composed of a first concave portion 56 b 1 that forms the upper portion thereof and a second concave portion 56 b 2 that forms the central and lower portions thereof in the vertical direction. The first concave portion 56 b 1 faces the inlet 52 a of the first container 52 across the guide member 58. In other words, the first concave portion 56 b 1 and the inlet 52 a of the first container 52 face each other with the guide member 58 being interposed between them.

The first concave portion 56 b 1 is curved downward in the arc shape from the inlet 52 a side to the discharge side (i.e., from the intake side to the discharge side). In this example, the first concave portion 56 b 1 has the function of receiving exhaust gas having flowed into the first chamber 61 from the inlet 52 a and guiding the gas downward (for example, to the second concave portion 56 b 2).

The lower end of the first concave portion 56 b 1 is continuous to the upper end of the second concave portion 56 b 2. The second concave portion 56 b 2 protrudes toward the discharge side as compared to the first concave portion 56 b 1. The second concave portion 56 b 2 has substantially a rectangular shape as viewed from the front as shown in FIG. 7. At least a portion (see, for example, portion P of FIG. 6) of its bottom 56 bt is in contact with the inner surface of the second container 53. In other words, at least a portion of the bottom 56 bt of the concave portion 56 b is in contact with the inner surface of the second chamber 62 in the housing 51. The bottom 56 bt constitutes an end wall on the discharge side, out of the second concave portion 56 b 2 of the concave portion 56 b.

The bottom 56 bt of the second concave portion 56 b 2 includes an exhaust gas passage forming portion 56 bt 1 that protrudes somewhat toward the discharge side. The exhaust gas passage forming portion 56 bt 1 blocks a portion of the above outlet 53 a (in the present embodiment, at least left portion). Here, the remaining portion of the outlet 53 a, which is not blocked by the exhaust gas passage forming portion 56 bt 1, constitutes a substantial opening 53 a 1 of the outlet 53 a. Furthermore, the exhaust gas passage forming portion 56 bt 1 corresponds to “a portion of the bottom of the concave portion, which partially blocks the outlet” of the present invention.

The second concave portion 56 b 2 has an exhaust gas guide portion 56 bt 2 adjoining the right side of the exhaust gas passage forming portion 56 bt 1. As illustrated in FIG. 7, the exhaust gas guide portion 56 bt 2 is formed like a groove that is recessed toward the first chamber 61 side as viewed from the front. The exhaust gas guide portion 56 bt 2 has the function of guiding the exhaust gas inside the second chamber 62 to the substantial opening 53 a 1 of the outlet 53 a.

As shown in FIG. 7, plural (ten in FIG. 7) through holes 57 are formed on the left side of the main body portion 56 a of the partition 56. In this example, the through holes 57 are positioned lower than the inlet 52 a of the first container 52. In FIG. 7, the ten through holes 57 are illustrated, but the number of through holes 57 is not limited to ten.

Also, in the present embodiment, as shown in FIG. 6, the concave portion 56 b (especially, second concave portion 56 b 2) is positioned between the outlet 53 a (especially, the substantial opening 53 a 1) and the plural through holes 57 in the horizontal direction (right-left direction). In the present embodiment, as shown in FIG. 7, a C-shaped region 56 bt 3 is in contact with the inner surface of the second chamber 62 in the housing 51. The region 56 bt 3 extends covering the upper side, the lower side, and the left side of the exhaust gas passage forming portion 56 bt 1 out of the bottom 56 bt of the second concave portion 56 b 2 of the concave portion 56 b.

The tubular exhaust gas passage 67 of the substantially rectangular cross-sectional shape is defined by the convex portion 53 p of the second container 53 and the exhaust gas passage forming portion 56 bt 1 of the second concave portion 56 b 2 of the partition 56. The exhaust gas passage 67 extends in the horizontal direction (right-left direction) and communicates with, on the right side thereof, the second chamber 62 through the outlet 53 a (especially, the substantial opening 53 a 1). The left end of the exhaust gas passage 67 corresponds to the above opening 53 q. The exhaust gas passage 67 serves to guide exhaust gas from the outlet 53 a (especially, the substantial opening 53 a 1) to the opening 53 q.

At least one (two in FIGS. 4 and 6) cylindrical portion 65 penetrates the housing 51. The cylindrical portion 65 is formed to penetrate the first container 52, the second container 53, and the partition 56. A bolt (not shown) for fixing the housing 51 to the engine 21 may be inserted into the cylindrical portion 65. Note that FIGS. 4 and 6 show the two cylindrical portions 65, but the number of cylindrical portions 65 is not limited to two. Also, FIG. 7 shows through holes 65 a in each of which the cylindrical portion 65 is inserted.

The guide member 58 is made of metal or resin and attached to the inlet 52 a of the first container 52. The guide member 58 has the U-shaped sectional shape that opens at its lower end and extends toward the discharge side from the inlet 52 a of the first container 52.

The guide member 58 has the function of smoothly guiding to the concave portion 56 b of the partition 56 the exhaust gas having flowed into the first chamber 61 through the inlet 52 a from the exhaust port 36.

In the present embodiment, the concave portion 56 b of the partition 56 (especially, the second concave portion 56 b 2) functions as a flow regulating part 70 so as to partially regulate the flow of the exhaust gas inside the second chamber 62. The flow regulating part 70 regulates, especially, the flow of the exhaust gas that flows straight inside the second chamber 62 from the through hole 57 to the outlet 53 a (especially, the substantial opening 53 a 1) in the horizontal direction. Moreover, in the present embodiment, the flow regulating part 70 partially constitutes the partition 56 (the concave portion 56 b (especially the second concave portion 56 b 2)). The flow regulating part 70 is interposed between the housing 51 (especially, the second container 53) and the partition 56 (especially, the main body portion 56 a) inside the second chamber 62.

In the present embodiment, as shown in FIG. 5, the partition 56 is placed in the housing 51 so that a flow direction F1 of the exhaust gas at the inlet 52 a of the first container 52 forms obtuse angle θ1 with a direction F2 extending from the lower end to the upper end of the main body portion 56 a of the partition 56. The obtuse angle θ1 is preferably within a range of 95° to 125°, more preferably 100° to 120°.

In the present embodiment, distance L1 is set longer than distance L2; the distance L1 is from a portion of the inner wall at the lower end of the first chamber 61, which faces the lower end of the main body portion 56 a of the partition 56, to the lower end of the main body portion 56 a of the partition 56, and the distance L2 is from a portion of the inner wall at the lower end of the second chamber 62, which faces the lower end of the main body portion 56 a of the partition 56, to the lower end of the main body portion 56 a of the partition 56. In addition, the partition 56 includes the concave portion 56 b. Thereby, the first chamber 61 can ensure large volume enough to let high-temperature and high-pressure exhaust gas flow in.

Next, the flow of the exhaust gas discharged to the outside from the exhaust port 36 via the muffler 50 is described. FIGS. 8A and 8B and FIGS. 9A, and 9B show the flow of exhaust gas inside the muffler 50 of the present embodiment. FIG. 8A corresponds to FIG. 5 as referenced above. FIG. 9A corresponds to FIG. 6 as referenced above. FIGS. 8B and 9B correspond to FIG. 7 as referenced above.

The flow direction of exhaust gas having flowed into the first chamber 61 from the exhaust port 36 through the inlet 52 a of the muffler 50 is directed downward by the concave portion 56 b of the partition 56 (especially, the first concave portion 56 b 1) (see flow S1 of the exhaust gas as indicated by arrows in FIGS. 8A and 8B). In this example, the concave portion 56 b of the partition 56 (especially, the first concave portion 56 b 1) can function to receive the exhaust gas having flowed into the first chamber 61 from the inlet 52 a and guide the gas downward.

After dispersed into the first chamber 61 and cooled, the exhaust gas passes through the through hole 57 of the partition 56 and flows into the left side of the second chamber 62 (see flow S2 of the exhaust gas as indicated by arrows in FIGS. 8A, 8B, and 9A). The exhaust gas having flowed into the left side of the second chamber 62 flows inside the second chamber 62 so as to pass above and below the concave portion 56 b of the partition 56 (especially, the second concave portion 56 b 2) and reaches the right side of the second chamber 62 (see flows S3 and S4 of the exhaust gas as indicated by arrows in FIGS. 9A and 9B). Note that the exhaust gas can be dispersed and cooled in the second chamber 62 as well.

Subsequently, the exhaust gas passes the exhaust gas guide portion 56 bt 2 of the partition 56 and the outlet 53 a (especially, substantial opening 53 a 1) and further the exhaust gas passage 67 and then is discharged from the opening 53 q of the exhaust gas passage 67 to the outside (see flow S5 of the exhaust gas as indicated by arrows in FIGS. 9A and 9B). Note that the first container 52, the second container 53, and the partition 56 receives heat of the exhaust gas passing through the muffler 50 and releases the received heat to the outside from outer surfaces of the first container 52 and the second container 53.

According to the present embodiment, the muffler 50 includes: the box-shaped housing 51 having the inlet 52 a that is connected to the exhaust port 36 of the engine 21 to allow the exhaust gas to flow in, and the outlet 53 a for discharging the exhaust gas having flowed in; and the partition 56 for dividing the inside of the housing 51 into the first chamber 61 with the inlet 52 a and the second chamber 62 with the outlet 53 a. The partition 56 includes the main body portion 56 a in the form of a flat plate and the concave portion 56 b protruding from the main body portion 56 a toward the second chamber 62 side. The main body portion 56 a has, on one side thereof (left side), at least one through hole 57 that communicates between the first chamber 61 and the second chamber 62. At least a portion of the bottom 56 bt (e.g., the region 56 bt 3) of the concave portion 56 b contacts the inner surface of the second chamber 62 in the housing 51. The exhaust gas, having flowed into the first chamber 61 from the inlet 52 a, passed the through hole 57, and reached one side (left side) in the second chamber 62, flows inside the second chamber 62 so as to bypass the concave portion 56 b (especially, second concave portion 56 b 2). Then, the gas passes the other side (right side) in the second chamber 62 to reach the outlet 53 a (especially, substantial opening 53 a 1) (see flows S1-S5 of the exhaust gas in FIGS. 8A and 8B and FIGS. 9A and 9B). This makes it possible to relatively increase the substantial distance the exhaust gas flows (moves), from the through hole 57 of the partition 56 to the outlet 53 a of the housing 51, contributing to efficient reduction of the exhaust gas pressure in the second chamber 62 and further to enhancement of the noise-reduction effect of the muffler.

According to the present embodiment, the concave portion 56 b (especially, second concave portion 56 b 2) is positioned between the outlet 53 a (especially, substantial opening 53 a 1) and the through hole 57. This makes it possible to ensure, with simple structure, the relatively long substantial distance the exhaust gas flows (moves), from the through hole 57 of the partition 56 to the outlet 53 a of the housing 51.

According to the present embodiment, the concave portion 56 b (especially, first concave portion 56 b 1) faces the inlet 52 a, whereby the concave portion 56 b (especially, first concave portion 56 b 1) can smoothly receive the exhaust gas having flowed from the inlet 52 a into the first chamber 61.

According to the present embodiment, the inlet 52 a is provided at an upper portion of the first chamber 61. The concave portion 56 b receives the exhaust gas having flowed from the inlet 52 a into the first chamber 61 and guides it downward. As a result, the exhaust gas can be appropriately dispersed and cooled inside the first chamber 61.

According to the present embodiment, the main body portion 56 a has the through hole 57 on one horizontal side thereof (left side). The exhaust gas, having flowed from the inlet 52 a into the first chamber 61, passed the through hole 57, and reached one horizontal side (left side) in the second chamber 62, flows inside the second chamber 62 so as to pass above and below the concave portion 56 b (especially, second concave portion 56 b 2), passes the other horizontal side (right side) in the second chamber 62, and reaches the outlet 53 a (especially, substantial opening 53 a 1) (see flows S1-S5 of the exhaust gas in FIGS. 8A and 8B and FIGS. 9A and 9B). This makes it possible to relatively increase the substantial distance the exhaust gas flows (moves), from the through hole 57 of the partition 56 to the outlet 53 a of the housing 51, contributing to efficient reduction of the exhaust gas pressure in the second chamber 62 and further to enhancement of the noise-reduction effect of the muffler.

According to the present embodiment, the housing 51 (especially, second container 53) includes the convex portion 53 p that protrudes outward to cover the outlet 53 a, and the convex portion 53 p has the opening 53 q. The tubular exhaust gas passage 67 for guiding the exhaust gas from the outlet 53 a (especially, substantial opening 53 a 1) to the opening 53 q is defined by the convex portion 53 p and a portion (exhaust gas passage forming portion 56 bt 1) of the bottom 56 bt of the concave portion 56 b, which partially blocks the outlet 53 a. Thus, an exhaust duct usually attached as an external member to the outer surface of the housing 51 (especially, second container 53) can be omitted and functionally replaced by the exhaust gas passage 67. The total number of components can be accordingly reduced by the number of components for the duct. Moreover, the portion functioning as the duct can be prepared only by combining the convex portion 53 p of the housing 51 and the exhaust gas passage forming portion 56 bt 1 of the partition 56, whereby the production time for the duct can be considerably reduced as compared to the conventional configuration.

According to the present embodiment, the muffler 50 includes: the box-shaped housing 51 having the inlet 52 a that is connected to the exhaust port 36 of the engine 21 to allow the exhaust gas to flow in, and the outlet 53 a for discharging the exhaust gas having flowed in; the partition 56 for dividing the inside of the housing 51 into the first chamber 61 with the inlet 52 a and the second chamber 62 with the outlet 53 a; and the flow regulating part 70 for partially regulating the flow of the exhaust gas inside the second chamber 62. The partition 56 has, on one side thereof (left side), at least one through hole 57 that communicates between the first chamber 61 and the second chamber 62. The exhaust gas having flowed from the inlet 52 a into the first chamber 61, passed the through hole 57, and reached one side (left side) in the second chamber 62, flows inside the second chamber 62 so as to bypass the flow regulating part 70 and then passes the other side (right side) in the second chamber 62 to reach the outlet 53 a (especially, substantial opening 53 a 1) (see flows S1-S5 of the exhaust gas in FIGS. 8A and 8B and FIGS. 9A and 9B). This makes it possible to relatively increase the substantial distance the exhaust gas flows (moves), from the through hole 57 of the partition 56 to the outlet 53 a of the housing 51, contributing to efficient reduction of the exhaust gas pressure in the second chamber 62 and further to enhancement of the noise-reduction effect of the muffler.

According to the present embodiment, the flow regulating part 70 is positioned between the outlet 53 a (especially, substantial opening 53 a 1) and the through hole 57. This makes it possible to ensure, with simple structure, the relatively long substantial distance the exhaust gas flows (moves), from the through hole 57 of the partition 56 to the outlet 53 a of the housing 51.

According to the present embodiment, the main body portion 56 a has the through hole 57 on one horizontal side thereof (left side). The exhaust gas, having flowed from the inlet 52 a into the first chamber 61, passed the through hole 57, and reached one horizontal side (left side) in the second chamber 62, flows inside the second chamber 62 so as to pass above and below the flow regulating part 70, passes the other horizontal side (right side) in the second chamber 62, and reaches the outlet 53 a (especially, substantial opening 53 a 1) (see flows S1-S5 of the exhaust gas in FIGS. 8A and 8B and FIGS. 9A and 9B). This makes it possible to relatively increase the substantial distance the exhaust gas flows (moves), from the through hole 57 of the partition 56 to the outlet 53 a of the housing 51, contributing to efficient reduction of the exhaust gas pressure in the second chamber 62 and further to enhancement of the noise-reduction effect of the muffler.

According to the present embodiment, the flow regulating part 70 partially constitutes the partition 56 (concave portion 56 b (especially, second concave portion 56 b 2)). This eliminates the necessity for preparing the flow regulating part 70 by use of any other member and consequently contributes to reduction in the total number of components.

According to the present embodiment, the flow regulating part 70 is positioned, inside the second chamber 62, between the housing 51 (especially, second container 53) and the partition 56 (especially, main body portion 56 a). Thus, the exhaust gas flowing from the left to the right inside the second chamber 62 can pass, in mid-flow, above and below the flow regulating part 70.

In the present embodiment, described is the case that the exhaust gas flowing from the left to the right inside the second chamber 62 passes, in mid-flow, above and below the flow regulating part 70 (concave portion 56 b of the partition 56 (especially, second concave portion 56 b 2)). As regards the bypass routes of the exhaust gas, however, the gas has only to pass either above or below the flow regulating part 70 (concave portion 56 b of the partition 56 (especially, second concave portion 56 b 2)). More specifically, the exhaust gas flowing from the left to the right inside the second chamber 62 can pass, in mid-flow, above or below the flow regulating part 70 (concave portion 56 b of the partition 56 (especially, second concave portion 56 b 2)).

In the present embodiment, the concave portion 56 b of the partition 56 (especially, second concave portion 56 b 2) is described as an example of the flow regulating part 70. However, the configuration of the flow regulating part 70 is not limited to the above.

As another example of the flow regulating part 70, the second container 53 can be, instead of forming the second concave portion 56 b 2 in the partition 56, integrally molded to include any substitute for the second concave portion 56 b 2. In this case, the flow regulating part 70 partially constitutes the housing 51 (especially, second container 53).

To give still another example of the flow regulating part 70, the partition 56 is composed of the plate-like main body portion 56 a alone and the aforementioned other member substitutable for the second concave portion 56 b 2 is interposed between the main body portion 56 a of the partition 56 and the inner surface of the second container 53. In this example, the aforementioned other member corresponds to the flow regulating part 70, which is disposed inside the second chamber 62, and which is held between the housing 51 (especially, second container 53) and the partition 56.

In the present embodiment, the brush/weed cutter is described as an example of the portable work machine in which the muffler 50 is installed. However, the muffler 50 can be installed in any other portable work machines. For example, the muffler 50 can be installed in portable work machines such as a hole-digging machine and a concrete cutter. Alternatively, the muffler 50 can be installed in backpack work machines such as a backpack blower, a sprayer (spray), a dust blower, and a backpack brush/weed cutter.

In the present embodiment, the OHV type 4-stroke engine is described as an example of the engine 21. However, the configuration of the engine 21 is not limited thereto. For example, the engine 21 could be an OHC-type engine.

In the present embodiment, the cylinder head 28 and the cylinder part 22 are separately provided in the engine 21 by way of example. Alternatively, the cylinder head and the cylinder part can be integrated.

In the muffler for an engine according to the first aspect of the present invention, at least a portion of the bottom of the concave portion of the partition is in contact with the inner surface of the second chamber in the housing. Moreover, the exhaust gas, having flowed from the inlet of the housing into the first chamber, passed the through hole of the partition, and reached one side in the second chamber, flows inside the second chamber so as to bypass the concave portion of the partition, passes the other side in the second chamber, and reaches the outlet of the housing. This makes it possible to relatively increase the substantial distance the exhaust gas flows (moves), from the through hole of the partition to the outlet of the housing, contributing to efficient reduction of the exhaust gas pressure in the second chamber and further to enhancement of the noise-reduction effect of the muffler.

In the muffler for an engine according to the second aspect of the present invention, the flow regulating part partially regulates the exhaust gas flow inside the second chamber. Furthermore, the exhaust gas, having flowed from the inlet of the housing into the first chamber, passed the through hole of the partition, and reached one side in the second chamber, flows inside the second chamber so as to bypass the flow regulating part, passes the other side in the second chamber, and reaches the outlet of the housing. This makes it possible to relatively increase the substantial distance the exhaust gas flows (moves), from the through hole of the partition to the outlet of the housing, contributing to efficient reduction of the exhaust gas pressure in the second chamber and further to enhancement of the noise-reduction effect of the muffler.

The embodiments of the present invention are described above but the present invention is not limited to these embodiments. As is needless to say, various changes and modifications can be made based on the technical idea of the present invention. 

What is claimed is:
 1. A muffler for an engine, comprising: a box-shaped housing having an inlet that is connected with an exhaust port of the engine to allow exhaust gas to flow in, and an outlet for discharging the exhaust gas having flowed in; and a partition for dividing the inside of the housing into a first chamber with the inlet and a second chamber with the outlet, wherein the partition includes a main body portion in the form of a flat plate, and a concave portion that protrudes toward the second chamber from the main body portion, the main body portion has, on one side thereof, at least one through hole that communicates between the first and second chambers, at least a portion of the bottom of the concave portion contacts an inner surface of the second chamber in the housing, and exhaust gas having flowed from the inlet into the first chamber, passed the through hole, and reached one side in the second chamber, flows inside the second chamber so as to bypass the concave portion and then passes the other side in the second chamber to reach the outlet.
 2. The muffler for an engine according to claim 1, wherein the concave portion is positioned between the outlet and the through hole.
 3. The muffler for an engine according to claim 1, wherein the concave portion faces the inlet.
 4. The muffler for an engine according to claim 3, wherein the inlet is formed at an upper portion of the first chamber, and the concave portion receives exhaust gas having flowed from the inlet into the first chamber and guides the gas downward.
 5. The muffler for an engine according to claim 1, wherein the main body portion has the through hole on one horizontal side thereof, and exhaust gas having flowed from the inlet into the first chamber, passed the through hole, and reached one horizontal side in the second chamber, flows inside the second chamber so as to pass above and/or below the concave portion and then passes the other horizontal side in the second chamber to reach the outlet.
 6. The muffler for an engine according to claim 1, wherein the housing includes a convex portion that protrudes outward so as to cover the outlet, and the convex portion has an opening, and a tubular exhaust gas passage for guiding exhaust gas from the outlet to the opening is defined by the convex portion and a portion of the bottom of the concave portion, which partially blocks the outlet.
 7. A muffler for an engine, comprising: a box-shaped housing having an inlet that is connected with an exhaust port of the engine to allow exhaust gas to flow in, and an outlet for discharging the exhaust gas having flowed in; a partition for dividing the inside of the housing into a first chamber with the inlet and a second chamber with the outlet; and a flow regulating part for partially regulating the flow of exhaust gas inside the second chamber, wherein the partition has, on one side thereof, at least one through hole that communicates between the first and second chambers, and exhaust gas having flowed from the inlet into the first chamber, passed the through hole, and reached one side in the second chamber, flows inside the second chamber so as to bypass the flow regulating part and then passes the other side in the second chamber to reach the outlet.
 8. The muffler for an engine according to claim 7, wherein the flow regulating part is positioned between the outlet and the through hole.
 9. The muffler for an engine according to claim 7, wherein the partition has, on one horizontal side thereof, the through hole, and exhaust gas having flowed from the inlet into the first chamber, passed the through hole, and reached one horizontal side in the second chamber, flows inside the second chamber so as to pass above and/or below the flow regulating part and then passes the other horizontal side in the second chamber to reach the outlet.
 10. The muffler for an engine according to claim 7, wherein the flow regulating part constitutes a portion of the partition or a portion of the housing.
 11. The muffler for an engine according to claim 7, wherein the flow regulating part is positioned inside the second chamber, between the housing and the partition. 